We shall examine the chemoreceptor responses of infants deemed at high-risk of SIDS. Groups of infants examined will include; infants born to maternal methadone-takers, infants who have experienced prolonged unexplained apneas (near-miss SIDS), and infants with bronchopulmonary dysplasia. We shall measure the ventilatory response to increasing concentrations of inspired carbon dioxide (1 to 4% in air). Measurements will also be made of EEG sleep state during chemoreceptor assessment and of cardiac rate variability in response to sound and airstream stimuli. The methodoloy employed also will allow measurement of oxygen consumption; carbon dioxide production; alveolar ventilation; anatomic deadspace; deadspace/tidal volume ration; and functional residual capacity (by nitrogen washout). In infants found to have reduced chemoreceptor function, we shall examine the effects of respiratory stimulants such as theophylline.